Method for manufacturing bladed members from powder material

ABSTRACT

The invention is concerned with manufacturing gas turbine engine components e.g. guide vanes and blades, in dense silicon nitride starting with silicon nitride in a powder form. Guide vanes are usually in the form of an aerofoil portion and two shroud portions and according to the invention, the aerofoil portion is made in a first mould by hot pressing a mixture of silicon nitride powder and a fluxing agent, such as magnesia. The formed aerofoil is placed in a second mould so that each end extends partly into a space which is to be filled with a further mixture of silicon nitride powder and a fluxing agent. The further mixtures are hot pressed both to form the shroud portions and to amalgamate the shroud portions with the aerofoil portion. Features, such as, flanges and webs can be formed in the shrouds during the moulding process or they can be machined into the shrouds after the vane is removed from the second mould.

United States Patent Bird Apr. 8, 1975 1 METHOD FOR MANUFACTURING BLADED MEMBERS FROM POWDER MATERIAL Primary Eraminen-Richard R. Kucia [75] Inventor: Jack Raymond Bird. cheuaston Attorney, Agent, or FtrmCushman. Darby &

Cushman England [73] Assignec: Rolls Royce (1971) Limited. [57] ABSTRACT London England The invention is concerned with manufacturing gas [22] Filed: Jan. 16, 1973 turbine engine components e.g. guide vanes and Appl. No.: 324,185

blades. in dense silicon nitride starting with silicon nitride in a powder form.

Guide vanes are usually in the form of an aerofoil portion and two shroud portions and according to the invention, the aerofoil portion is made in a first mould by hot pressing a mixture of silicon nitride powder and a fluxing agent. such as magnesia. The formed aerofoil is placed in a second mould so that each end extends partly into a space which is to be filled with a further mixture of silicon nitride powder and a fluxing agent. The further mixtures are hot pressed both to form the shroud portions and to amalgamate the shroud portions with the aerofoil portion.

Features, such as. flanges and webs can be formed in the shrouds during the moulding process or they can be machined into the shrouds after the vane is removed from the second mould.

5 Claims. 4 Drawing Figures PATENTEDAPR 8I975 METHOD FOR MANUFACTURING BLADED MEMBERS FROM POWDER MATERIAL This invention relates to a method for making bladed members from powder material. The invention is par ticularly though not exclusively concerned with the manufacture of nozzle guide vanes for gas turbine engines in hot pressed dense silicon nitride.

Throughout this specification the term hot pressed dense silicon nitride refers to the method of forming silicon nitride powder as described and claimed in UK. Pat. specification No. 970.639.

Nozzle guide vanes usually comprise an aerofoil portion. an inner shroud portion and an outer portion and the shroud portions usually differ in thickness from the aerofoil portion. The different thicknesses of the various portions of the vane prevents homogenous densification of the vane during manufacture as a one piece moulding. The thicker portions will not completely densify and cracking may occur due to internal stresses between sections of different density. For instance elastic moduli. thermal conductivity and strength vary di rectly with changing density.

The present invention seeks to provide a method of making a bladed member. such as a nozzle guide vane which overcomes the above difficulties.

Accordingly. the present invention provides a method of making a bladed member. the member including an aerofoil portion and at least one shroud portion. the method including the steps of hot pressing a first mixture of silicon nitride powder and a fluxing agent in a suitably shaped first mould to form the aerofoil portion. placing the formed aerofoil portion in locating means. the aerofoil portion extending partly from one end at least of the locating means. placing the locating means in a second mould. placing a second mixture of silicon nitride powder and a fluxing agent in a suitably shaped portion of the second mould. the aerofoil portion extending into the second powder mixture. hot pressing the second powder mixture to form the shroud portion and simultaneously to amalgamate the shroud portion with the aerofoil portion.

Generally the bladed member will have two shroud portions and the second mould will therefore have two suitably shaped portions in which the two shroud portions can be formed.

The shroud portion or portions can be partly preformed by hot pressing parts of the or each shroud beforehand and attaching these pre-formed parts to a plunger which is adapted to compress the second powder mixture.

The pre-formed parts may be formed with fixing means which may include features such as. flanges, webs, dowels and apertures so that completed bladed members can be readily secured within a structure such as a gas turbine engine.

Alternatively. the pre-formed parts can be omitted and the plunger may either have a plain face or may be shaped to produce fixing means as above defined in the completed shroud or shrouds.

The invention will now be particularly described with reference to the accompanying drawings in which:

FIG. I shows a plan of one form of mould which can be used for performing the method according to the present invention.

FIGS. 2. 3 and 4 show elevations of the mould shown in FIG. 1 at various stages of performing the method according to the present invention.

The invention will now be initially described with reference to the manufacture of hot pressed dense silicon nitride nozzle guide vanes for use in gas turbine engines.

The nozzle guide vane 2 as shown in FIG. 4 consists of an aerofoil portion 4. a root shroud portion 6 and an outer shroud portion 8.

Referring to the Figs. generally. a mould 10 consists ofa susceptor 12.21 packing ring 14 (FIG. 2) on which the susceptor stands. a split die 16, a locating plunger 18 (FIG. 2) an outer shroud plunger 20. a root shroud plunger 22 and a split aerofoil die 24.

Referring to FIG. 2 particularly. the aerofoil portion 4 is preformed by hot pressing a mixture of silicon nitride powder and magnesium oxide in a suitably shaped die. The pressing is preferably carried out at about L200 psi. and at a temperature of about l.75l) C. This method of forming silicon nitride articles is described in detail in UK. Pat. specification No. 970.369 and use of the mctod produces dense. compact silicon nitride articles ofalmost maximum theoretical density.

The pre-formed portion 4 is placed in the split aerofoil die 24 so that a small portion of the aerofoil extends beyond each end of the die. The die is then placed in a rectangular aperture 26 in the die 16 and is located on a shoulder 28. the lower end of the aerofoil resting on the locating plunger 18.

The space above the aerofoil portion 4 is filled with a mixture of silicon nitride powder and magnesium oxide in the ratio 20 to l by weight. this powder mixture being eventually to form the root shroud portion 6. The amount of powder mixture used depends on the depth ofthe formed root shroud which is required. The root shroud plunger 22 has a preformed root shroud portion 30 lightly attached to it. the portion 30 being of dense silicon nitride and formed by the method de scribed above. The plunger 22 is placed in the aperture and the powder mixture is lightly comptacted at normal temperature.

The mould 10, in the configuration shown in FIG. 3 is placed in a press (not shown) and a pressure of about 1,200 psi. is applied at a temperature of about l.750 C. The powder mixtures above and below the aerofoil densify to form the inner and outer shroud portions 6 and 8 respectively. All the preformed portions 30 and 32 amalgamate with the shroud portions 6 and 8 re spectively and the aerofoil portion 4 amalgamates with the shroud portions. A section taken through the completed nozzle guide vane shows that there is virtually no change in the structure across the boundaries between the pre-formed portions of the vane and the shroud portions which are formed in the final pressing action.

Various modifications of the method described above are possible within the scope of the present invention. The preformed portions of the inner and outer shrouds may be omitted or these pre-formed portions may be formed with fixing means. so that the formed bladed member may be readily attached to the engine structure. Such fixing means typically comprise features such as flanges. webs. apertures and dowels or any combination of these features. Alternatively. the plungers may be formed so that any of these features can be produced on either or both shrouds.

Also the bladed member may be formed with only one of the shroud portions. e.g. the root shourd. in which case. the final configuration of the mould is as shown in FIG. 2.

What I claim is:

l. A method of making a bladed member. the member including an aerofoil section and at least one shroud portion. the method including the steps of hot pressing a first mixture of nitride powder and a fluxing agent in a suitably shaped first mould to form said aerofoil portion placing the formed aerofoil portion in locating means. the aerofoil portion extending partly from one end at least of the locating means. placing the locating means in a second mould. placing a second mixture of silicon nitride powder and fluxing agent in a suitably shaped portion of the second mould, the aerofoil portion extending into said second mixture. hot pressing the second mixture to form the shroud portion and to amalgamate the shroud portion with the aerofoil portion.

2. A method as claimed in claim 1 in which the bladed member has two shroud portions, an inner shroud and an outer shroud portion. the second mould having two suitably shaped portions. the method including the steps of placing pre-determined quantities of said second powder mixture in the two suitably shaped portions of the second mould, hot pressing the second powder mixture to form the inner and outer shroud portions and to amalgamate said shroud portions with the aerofoil portion.

3. A method as claimed in claim 1 in which a portion of at least one of said two shroud portions is pre-formed by hot pressing a mixture of silicon nitride powder and a t'luxing agent in a suitably shaped mould.

4. A method as claimed in claim 3 in which the mould for the pre-formed shroud portion is formed so that the pre-formed shroud portion is formed with fixing means.

5. A method as claimed in claim 1 in which the second powder mixture is lightly compacted at normal temperature prior to hot pressing. 

1. A METHOD OF MAKING A BLADED MEMBER, THE MEMBER INCLUDING AN AEROFOIL SECTION AND AT LEAST ONE SHROUD PORTION, THE METHOD INCLUDING THE STEPS OF HOT PRESSING A FIRST MIXTURE OF NITRIDE POWDER AND A FLUXING AGENT IN A SUITABLY SHAPED FIRST MOULD TO FORM SAID AEROFOIL PORTION PLACING THE FORMED AEROFOIL PORTION IN LOCATING MEANS, THE AEROFOIL PORTION EXTENDING PARTLY FROM ONE END AT LEAST OF THE LOCATING MEANS, PLACING THE LOCATING MEANS IN A SECOND MOULD, PLACING A SECOND MIXTURE OF SILICON NITRIDE POWDER AND FLUXING AGENT IN A SUITABLY SHAPED PORTION OF THE SECOND MOULD, THE AEROFOIL PORTION EXTENDING INTO SAID SECOND MIXTURE, HOT PRESSING THE SECOND MIXTURE TO FORM THE SHROUD PORTION AND TO AMALGAMATE THE SHROUD PORTION WITH THE AEROFOIL PORTION.
 2. A method as claimed in claim 1 in which the bladed member has two shroud portions, an inner shroud and an outer shroud portion, the second mould having two suitably shaped portions, the method including the steps of placing pre-determined quantities of said second powder mixture in the two suitably shaped portions of the second mould, hot pressing the second powder mixture to form the inner and outer shroud portions and to amalgamate said shroud portions with the aerofoil portion.
 3. A method as claimed in claim 1 in which a portion of at least one of said two shroud portions is pre-formed by hot pressing a mixture of silicon nitride powder and a fluxing agent in a suitably shaped mould.
 4. A method as claimed in claim 3 in which the mould for the pre-formed shroud portion is formed so that the pre-formed shroud portion is formed with fixing means.
 5. A method as claimed in claim 1 in which the second powder mixture is lightly compacted at normal temperature prior to hot pressing. 